As the baby boom generation ages and retires, immigrants to the U.S. or U.S. born citizens with immigrant parents will make up the majority of working-age population growth, increasing by 17.6 million new immigrants by 2035 resulting in a working age population of 183 million, Pew Research reports. Without immigration, the U.S. workforce would decline from 173 million in 2015 to just 166 million in 2035.